High impedance rf filter for heater with impedance tuning device

ABSTRACT

Embodiments provide a plasma processing apparatus, substrate support assembly, and method of controlling a plasma process. The apparatus and substrate support assembly include a substrate support pedestal, a tuning assembly that includes a tuning electrode that is disposed in the pedestal and electrically coupled to a radio frequency (RF) tuner, and a heating assembly that includes one or more heating elements disposed within the pedestal for controlling a temperature profile of the substrate, where at least one of the heating elements is electrically coupled to an RF filter circuit that includes a first inductor configured in parallel with a formed capacitance of the first inductor to ground. The high impedance of the RF filters can be achieved by tuning the resonance of the RF filter circuit, which results in less RF leakage and better substrate processing results.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 16/188,678, filed Nov. 13, 2018, which is a Continuation ofco-pending U.S. patent application Ser. No. 14/228,227, filed Mar. 27,2014, which claims benefit of U.S. Provisional Patent Application Ser.No. 61/805,872, filed Mar. 27, 2013, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention generally relate to an apparatusand method for processing substrates.

Description of the Related Art

In the manufacture of integrated circuits and other electronic devices,plasma processes are often used for deposition or etching of variousmaterial layers. Plasma processing offers many advantages over thermalprocessing. For example, plasma enhanced chemical vapor deposition(PECVD) allows deposition processes to be performed at lowertemperatures and at higher deposition rates than achievable in analogousthermal processes. Thus, PECVD is advantageous for integrated circuitand flat panel display fabrication with stringent thermal budgets, suchas for very large scale or ultra-large scale integrated circuit (VLSI orULSI) device fabrication.

Plasma processing, such as plasma enhanced chemical vapor deposition(PECVD), is used to deposit materials, such as blanket dielectric filmson substrates, such as semiconductor wafers. A challenge for currentplasma processing chambers and processes includes controlling criticaldimension uniformity during plasma deposition processes. A particularchallenge includes substrate center to edge thickness uniformity infilms deposited using current plasma processing chambers and techniques.

One problem that has been encountered with plasma processing inintegrated circuit fabrication is that devices may become damaged as aresult of exposure to non-uniform plasma conditions, such as electricfield gradients. The susceptibility or degree of device damage dependson the stage of device fabrication and the specific device design.Devices containing an insulating or dielectric layer deposited on asubstrate are susceptible to damage due to charges and/or potentialgradients accumulating on the surface of the dielectric layer.

Therefore, there is a need for an improved method and apparatus forplasma processing.

SUMMARY OF THE INVENTION

In one embodiment, a plasma processing apparatus includes a chamber bodyand a powered gas distribution manifold enclosing a process volume, anda pedestal disposed in the process volume for supporting a substrate.The apparatus further includes a tuning assembly that includes a tuningelectrode that is disposed in the pedestal and electrically coupled to aradio frequency (RF) tuner, and a heating assembly that includes one ormore heating elements disposed within the pedestal for controlling atemperature profile of the substrate, where at least one of the heatingelements is electrically coupled to an RF filter circuit that includes afirst inductor configured in parallel with a formed capacitance of thefirst inductor to ground.

In another embodiment, a substrate support assembly includes a substratesupport pedestal, a tuning assembly that includes a tuning electrodethat is disposed in the pedestal and electrically coupled to a radiofrequency (RF) tuner, and a heating assembly that includes one or moreheating elements disposed within the pedestal for controlling atemperature profile of the substrate, where at least one of the heatingelements is electrically coupled to an RF filter circuit that includes afirst inductor configured in parallel with a formed capacitance of thefirst inductor to ground.

In another embodiment, a method is provided of controlling a plasmaprocess using a tuning circuit, and a radio frequency (RF) filtercircuit coupled to a heater circuit. The method includes controlling animpedance of the tuning circuit to increase the amount of RF energydelivered to a tuning electrode of the tuning circuit, and using the RFfilter circuit to prevent RF energy from coupling to the heater circuit,where the RF filter circuit comprises a first inductor configured inparallel with a formed capacitance of the first inductor to ground.

Embodiments of the disclosure may further provide a plasma processingapparatus, comprising a chamber body and a powered gas distributionmanifold enclosing a process volume, a pedestal disposed in the processvolume and having a substrate supporting surface, a heating assemblycomprising one or more heating elements disposed within the pedestal forcontrolling a temperature profile of the substrate, wherein at least oneof the heating elements is electrically coupled to a radio frequency(RF) filter circuit comprising a first inductor configured in parallelwith a first capacitance, and a tuning assembly comprising a tuningelectrode that is disposed within the pedestal between the one or moreheating elements and the substrate supporting surface, wherein thetuning electrode is electrically coupled to a first RF tuner.

Embodiments of the disclosure may further provide a substrate supportassembly, comprising a substrate support pedestal having a substratesupporting surface, a heating assembly comprising one or more heatingelements disposed within the pedestal for controlling a temperatureprofile of the substrate, wherein at least one of the heating elementsis electrically coupled to a radio frequency (RF) filter circuitcomprising a first inductor configured in parallel with a firstcapacitance, and a tuning assembly comprising a tuning electrode that isdisposed within the pedestal and is electrically coupled to an RF tuner.

Embodiments of the disclosure may further provide a method of plasmaprocessing a substrate, comprising generating an RF plasma in aprocessing volume of a processing chamber, controlling an impedance ofthe tuning circuit, wherein controlling the impedance includesminimizing the impedance of a tuning electrode disposed within asubstrate supporting pedestal to ground, and reducing RF couplingbetween a heater element disposed within the substrate supportingpedestal and the generated RF plasma, wherein reducing the RF couplingto the heater element comprises coupling an RF filter circuit thatcomprises a first inductor that is in parallel with a first capacitanceto the heater element.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic depiction of a plasma processing apparatus,according to one embodiment described herein.

FIG. 2 is a schematic depiction of a substrate support pedestal,according to one embodiment described herein.

FIG. 3 illustrates a bottom view of a substrate support pedestal base,according to one embodiment described herein.

FIG. 4 is an electrical circuit diagram for an RF filter, according toone embodiment described herein.

FIG. 5 illustrates a filter response of an RF filter, according to oneembodiment described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation. The drawings referred to here should not beunderstood as being drawn to scale unless specifically noted. Also, thedrawings are often simplified and details or components omitted forclarity of presentation and explanation. The drawings and discussionserve to explain principles discussed below, where like designationsdenote like elements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or in the following detailed description.

Greater uniformity in deposited and/or etched films may be achievedthrough greater control of the process variables and application ofprocess inputs, such as RF energy and substrate thermal control. RFenergy is typically delivered to a powered electrode, and an RF field isestablished between the powered electrode and a grounding electrode. TheRF field is combined with process gases to deposit layers of materialonto a substrate or etch material layers from the substrate. Ascomponents used to control the temperature of the substrate duringprocessing may be disposed near the grounding electrode, RF energy maycapacitively couple to the heating elements, normally referred to as RFleakage. RF leakage to these undesired paths, such as heating elementsmay negatively alter the substrate processes (i.e., deposition rate anduniformity) and may also cause electromagnetic interference (EMI) withinand/or damage the AC power sources.

According to various embodiments, a substrate support pedestal mayinclude a tuning electrode 112 (such as a conductive mesh) providing aprimary path to ground for RF energy. The tuning electrode may becoupled to an RF tuner to present a lower impedance path and therebyprevent RF leakage into other components within the substrate supportpedestal. The substrate support pedestal may also include a heatingassembly that includes heating elements 150 and one or more conductiverods (e.g., rods 122, 155) disposed along the length of the shaft of thepedestal (e.g., stem 114). The conductive rods may be preferentiallyspaced apart to prevent undesired coupling to other rods or to otherconductive components, such as the pedestal base. The heating assemblymay include an AC source 165 that is coupled to the rods through one ormore RF filters 160. In order to minimize the impedance of theconnections between the rods and RF filters, the RF filters may bedisposed proximate to the pedestal base and coupled using a short rigidlead for each rod. Each lead may be spaced apart to prevent couplingwith other leads. The RF filters may generally block RF leakage intocomponents of the heating assembly, increasing process efficiency andimproving process results (e.g., uniformity) and preventing the RFenergy from causing EMI within and/or damage to the AC source. Thecomponents of the RF filters may be selected to provide a desiredimpedance value at the RF operating frequencies, and may compensate forcapacitances of the filter components (such as intra-windingcapacitance, parasitic capacitance, and coupling to other components).

FIG. 1 is a schematic side cross-sectional depiction of a plasmaprocessing apparatus, according to one embodiment described herein. Theapparatus includes a chamber 100 in which one or more films may bedeposited on or etched from a substrate 110 disposed on a substratepedestal 108. The chamber includes a chamber body 102 and a gasdistribution assembly 104, which distributes gases uniformly into aprocess volume 106. The substrate pedestal 108, hereafter pedestal 108,is disposed within the process volume 106 and supports the substrate110. The pedestal 108 includes a heating element 150. The pedestal 108is movably disposed in the process volume 106 by a stem 114 that extendsthrough the chamber body 102, where it is connected to a drive system103 and bellows to allow the pedestal 108 to be raised, lowered, and/orrotated.

The gas distribution assembly 104 includes a gas inlet passage 116,which delivers gas from a gas flow controller 120 into a gasdistribution manifold 118. The gas distribution manifold 118 includes aplurality of holes or nozzles (not shown) through which gaseous mixturesare injected into the process volume 106 during processing.

A high frequency RF power source 126 and a low frequency RF power source127 provide electromagnetic energy through a match circuit 129 to powerthe gas distribution manifold 118, which acts as an RF poweredelectrode, to facilitate generation of a plasma within the processvolume 106 between the gas distribution manifold 118 and the pedestal108. The pedestal 108 includes a tuning electrode 112, which iselectrically grounded through an RF rod 122, such that an electric fieldis generated in the chamber 100 between the powered gas distributionmanifold 118 and the tuning electrode 112. In one embodiment, the tuningelectrode 112 comprises a conductive mesh, such as a tungsten ormolybdenum containing mesh that is disposed within the dielectricmaterial that is used to form the pedestal 108. In one configuration,the pedestal 108 includes a ceramic material, such as aluminum nitride(AlN), silicon nitride (SiN), silicon carbide (SiC) or the like.

A ceramic ring 123 is positioned below the gas distribution manifold118. Optionally, a tuning ring 124 is disposed between the ceramic ring123 and an isolator 125, which electrically isolates the tuning ring 124from the chamber body 102. The tuning ring 124 is typically made from aconductive material, such as aluminum, titanium, or copper. As depictedin FIG. 1, the optional tuning ring 124 is positioned concentricallyabout the pedestal 108 and substrate 110 during processing of thesubstrate 110. The tuning ring 124 is electrically coupled to an RFtuner 135, which includes a variable capacitor 128, such as a variablevacuum capacitor, that is terminated to ground through an inductor L1.RF tuner 135 also includes a second inductor L2 that is electricallycoupled in parallel to the variable capacitor 128 to provide a path forlow frequency RF to ground. RF tuner 135 also includes a sensor 130,such as a voltage/current (V/I) sensor, that is positioned between thetuning ring 124 and the variable capacitor 128 for use in controllingthe current flow through the tuning ring 124 and the variable capacitor128.

The tuning electrode 112 formed in the pedestal 108 is electricallycoupled through RF rod 122 to an RF tuner 145, which includes a variablecapacitor 139, such as a variable vacuum capacitor, that is terminatedto ground through an inductor L3. RF tuner 145 also includes a secondinductor L4 that is electrically coupled in parallel to the variablecapacitor 139 to provide a path for low frequency RF to ground. RF tuner145 also includes a sensor 140, such as a V/I sensor, that is positionedbetween the tuning electrode 112 and the variable capacitor 139 for usein controlling the current flow through the tuning electrode 112 and thevariable capacitor 139.

One or more heating elements 150 are disposed within the pedestal 108and are used to control a temperature profile across the substrate 110.As depicted, the heating elements 150 may be disposed beneath the tuningelectrode 112; in other words, the tuning electrode 112 is disposedcloser to the substrate than the heating elements 150. The heatingelements 150 generally provide resistive heating to the substrate 110,and may be comprised of any feasible material, such as a conductivemetal wire (e.g., refractory metal wire), patterned metal layer (e.g.,molybdenum, tungsten or other refractory metal layer) or other similarconductive structure. The heating elements 150 are connected to one ormore conductive rods 155, which may extend along the length of the stem114 of the pedestal 108. In one embodiment, the rods 155 are positionedsubstantially parallel to the RF rod 122. The rods 155 couple theheating elements 150 to a heating power source 165, through one or moreRF filters 160. The rods 122 and 155 are generally solid conductiveelements (e.g., moderate diameter solid wire, non-stranded wire) thatare formed from a conductive material, such as copper, nickel, gold,coated aluminum, a refractory metal or other useful material. The RFfilters 160 are generally either low-pass filters or band-stop filtersthat are configured to block RF energy from reaching the heating powersource 165. The configuration of the RF filters 160 will be discussed infurther detail below. In one embodiment, the heating power source 165provides a non-RF, alternating current (AC) power to the heatingelements 150. For example, the heating power source 165 may providethree-phase AC power at a frequency of approximately 60 Hertz.

A system controller 134 controls the functions of the variouscomponents, such as the RF power sources 126 and 127, the drive system103, the variable capacitors 128 and 139, and heating power source 165.The system controller 134 executes system control software stored in amemory 138. The system controller 134 comprises parts of or all of oneor more integrated circuits (ICs) and/or other circuitry components. Thesystem controller 134 may in some cases include a central processingunit (CPU) (not shown), memory (not shown), and support circuits (orI/O) (not shown). The CPU may be one of any form of computer processorthat is used for controlling various system functions and supporthardware and monitoring the processes being controlled by and within thechamber 100. The memory is coupled to the CPU, and may be one or more ofa readily available memory, such as random access memory (RAM), readonly memory (ROM), floppy disk, hard disk, or any other form of digitalstorage, local or remote. Software instructions (or computerinstructions) and data may be coded and stored within the memory forinstructing the CPU. The software instructions may include a programthat determines which tasks are to be performed at any instant in time.The support circuits are also connected to the CPU for supporting theprocessor in a conventional manner. The support circuits may includecache, power supplies, clock circuits, timing circuits, input/outputcircuitry, subsystems, and the like.

In the plasma processing apparatus, chamber 100, an RF path isestablished between the powered gas distribution manifold 118 and thetuning electrode 112 via plasma. Further, by changing the capacitance ofthe variable capacitor 139, the impedance for the RF path through thetuning electrode 112 changes, in turn, causing a change in the RF fieldcoupled to the tuning electrode 112 and a change in the RF returncurrent through the tuning electrode 112 and the rod 122. Therefore, theplasma in the process volume 106 may be modulated across the surface ofthe substrate 110 during plasma processing. Controlling the RF field andmodulating the RF return current may thus result in higher processingrate in depositing films onto or etching material from the substrate 110with improved center-to-edge deposition thickness uniformity or etchremoval uniformity.

Further, an additional RF path is established between the powered gasdistribution manifold 118 and the tuning ring 124. Additionally, bychanging the capacitance of the variable capacitor 128, the impedancefor the RF path through the tuning ring 124 changes, in turn, causing achange in the RF field coupled to the tuning ring 124. For example, amaximum current and corresponding minimum impedance of the tuning ring124 can be achieved by varying the total capacitance of the variablecapacitor 128. Therefore, the plasma in the process volume 106 may alsobe modulated across the surface of the substrate 110 using thisadditional RF path.

During operation of the plasma processing apparatus, RF energy isnormally delivered to a top, powered electrode (i.e., the powered gasdistribution manifold 118), coupled through the plasma formed in theprocess volume 106 and the wafer and mainly returned through the wall ofthe chamber body 102 and/or tuning electrode 112 to ground. Sinceheating elements 150 may be embedded beneath the tuning electrode 112,RF energy can capacitively couple through the ceramic materials to theheating elements (i.e., RF leakage). The RF leakage to these undesiredpaths, such as heating elements and AC lines, not only affects thesubstrate processing results (i.e., deposition rate and uniformity onthe substrate) but also cause electromagnetic interference (EMI) on ordamage to the heating element AC power sources.

By adjusting the RF tuner 145 (and especially variable capacitor 139) tocompensate for the net reactance caused by other tuning assemblycomponents (e.g., tuning electrode 112, rod 122) at an operatingfrequency of the powered gas distribution manifold, a minimum impedancepath through the tuning assembly may be provided to ground. Thus, agreater proportion of RF energy will be coupled through this path, whichincludes the tuning electrode, rod 122 and RF tuner 145, with less RFleakage into other components of the plasma processing apparatus. Theminimum impedance path provides greater efficiency as well as greatercontrol of the application of RF energy for depositing films onto oretching material from the substrate. However, typically due to the needto use a mesh type of tuning electrode 112 within the pedestal 108 formanufacturing reasons, and the need to position the heating elements 150near the substrate supporting surface of the pedestal 108, unavoidablyan amount of the RF energy provided to the process volume 106 leaks tothe heating elements 150.

Conversely, the RF filters 160 may be included in the heating assemblyto provide a relatively greater impedance path to ground to minimize theamount of RF leakage to the heating elements 150. The RF filters 160 maybe inserted in between heating elements 150 and the corresponding ACsource(s) to attenuate RF energy and to suppress RF leakage current. Insome configurations, the impedance of the tuning electrode 112 to groundis substantially less than the impedance of the heating elements 150 toground.

FIG. 2 is a schematic depiction of a substrate support pedestal 108,according to one embodiment described herein. The substrate supportpedestal 108 may generally be used in a plasma processing apparatus,such as the apparatus described above with respect to FIG. 1.

Pedestal 108 is connected to stem 114, which may be constructed of aninsulative material, such as a ceramic (e.g., AlN, SiC, quartz). Thestem 114 in turn is connected to a pedestal base 230, which may beconstructed of a material, such as aluminum, stainless steel, or otherdesirable material.

Pedestal 108 includes a tuning assembly comprising tuning element 112,RF rod 122, and RF tuner 145. Pedestal 108 also includes a heatingassembly comprising a plurality of heating elements 150. The heatingelements may be distributed among a plurality of heating zones that areused to adjust the temperature profile across the substrate duringprocessing. The plurality of heating zones may include an inner zone 210and outer zone 220. The heating elements 150 are coupled through rods155 to one or more RF filters 160; the four rods 155 shown in FIG. 2 arereferred to in subsequent figures as A1, A2, B1, and B2. In oneembodiment, each of the rods 155 is coupled to a respective RF filter160, which may have the same or different properties. Groups of rods maycorrespond to different heating zones; for example, rods A1 and A2correspond to the heating elements of inner zone 210, while rods B1 andB2 correspond to heating elements of outer zone 220. In one embodiment,two rods 155 correspond to a particular zone. For example, the heatingpower source 165 delivers AC power through RF filters 160 into a firstrod of the two rods; the AC power travels through the first rod andheating elements 150 before returning through the second rod and RFfilters 160 to ground.

Components of the heating assembly will generally have a non-zeroimpedance that reflects both the intrinsic electrical properties of thecomponents and the proximity to other components in the pedestal orplasma processing apparatus. For example, heating elements 150 and rods155 may couple RF energy from tuning assembly components duringoperation. The resistive portion of components' impedance is typically anon-zero value that is not affected by changes in operating frequencyand is not able to be compensated for during processing. Therefore, forease of description, resistive components are not depicted in thisfigure.

The impedance of the heating elements 150 and rods 155 may thus bemodeled as including an inductive element and a capacitive element thatreflect the RF coupling to one or more components. For example, theimpedance of rod A1 includes a capacitance C4 reflecting a coupling ofrod A1 with components of the tuning assembly (i.e., with tuningelectrode 112 and RF rod 122), and includes an inductance L5 reflectinginductive properties of the inner zone 210 heating elements and the rodA1, as well as the inductive coupling caused by relatively large currentflow through the primary RF return path (i.e., RF rod 122). Rod A2 maygenerally have the same electrical properties as rod A1 and may bedisposed similarly, so that rod A2 is also modeled with capacitance C4and inductance L5. Of course, rods B1 and B2 may share electricalproperties, which may differ from rods A1 and A2, and thus rods B1 andB2 and outer zone 220 heating elements may each be modeled using acapacitance C5 and an inductance L6.

As shown, each of rods B1 and B2 also include a capacitance C6 thatrepresents a coupling between the rod and the typically groundedpedestal base 230. As rods A1 and A2 may have electrical properties anddispositions differing from rods B1 and B2, rods A1 and A2 may also havea coupling (not shown) with the pedestal base 230 that may differ fromcapacitance C6, or may be negligibly small.

To provide greater efficiency and greater control of the application ofRF energy for depositing films onto or removing material from asubstrate, ideally a maximum amount of the RF energy delivered by thepowered gas distribution manifold will be coupled through the wall ofthe chamber body 102 and tuning assembly to ground, with no chargecoupled into the heating assembly or into other components (i.e., RFleakage). Therefore, it is advantageous to reduce the impedance of thetuning assembly to a minimum value, and to increase the impedance of theheating assembly (e.g., heating elements 150 and one or more conductiverods). As discussed above, the components may all include some real,non-zero impedance (i.e., resistance) that cannot be compensated forduring processing. However, the reactance of different components may becontrolled by adjusting capacitive or inductive elements within thetuning assembly and the heating assembly.

To reduce the impedance of the tuning assembly to a minimum value andthereby couple more of the delivered RF energy into the tuning assembly,components of RF tuner 145 may be adjusted to compensate for thereactance of the tuning assembly components at the operating frequency.For example, the capacitance of variable capacitor 139 may be tuned whenthe tuning assembly has a positive reactance value for a particularfrequency. The negative reactance provided by the variable capacitor 139may thus compensate for the positive reactance.

To increase the impedance of the heating assembly, one or more RFfilters 160 are coupled to the rods 155 (as shown, rods A1, A2, B1, B2).The RF filters are either low-pass filters or band-stop filters that areconfigured to block RF energy from reaching the heating power source165.

The RF filters 160 may be coupled to rods 155 though conductiveconnections 240 near the pedestal base 230. In one embodiment, theconnections 240 may include a short rigid lead for each rod, so thateach RF filter 160 is directly coupled to each respective rod ordisposed proximate to the pedestal base 230 and to the respective rods.Further, each connection 240 may be maximally spaced apart to minimizecapacitive coupling between connections. It is believed that connectionsthat include a flexible and/or shielded multi-conductor cable disposedbetween the rods and the filter may introduce additional impedance andmay provide a shunt path for RF or other signals, as each conductor willhave resistive properties and may have coupling with the otherconductors and with the grounded shield. Therefore, in some embodiments,it is desirable to position the RF filter as close to the rods asmechanically feasible, and in some cases directly coupling the RF filterto each of the rods.

FIG. 3 illustrates a bottom view of a substrate support pedestal base230, according to one embodiment described herein. The pedestal base 230includes a bottom surface 305 and a cutout portion 310 that extendspartially into the pedestal base (as viewed, extending into the page)within which end portions of rods A1, A2, B1, and B2 are disposed. Ofcourse, bottom surface 305 may include other cutouts or mechanicalconnections for the pedestal base 230.

The rods A1, A2, B1, and B2 generally extend along the length of thepedestal stem 114 to the heating elements 150. To pass from the cutoutportion 310 through the pedestal base 108, each rod may extend through arespective opening (not shown) in the pedestal base in the area ofcutout portion 310. In order to prevent the rods from electricallyshorting to the pedestal base 230 (which may be grounded), an insulatingdevice (such as a ceramic tube; not shown) may be disposed in eachopening between the rods A1-B2 and the pedestal base 230. To provideadditional lateral support, a ceramic disk 320 may be disposed in thecutout portion 310 for supporting and electrically isolating the rods.

Within the cutout portion 310, each rod may be disposed to maintain atleast a minimum distance drod from the other rods. The distance drod maybe selected to provide a desired capacitive coupling between two rods(or between a rod and RF rod 122 (not shown in FIG. 3)), or to minimizethe capacitive coupling. The rods may also be disposed at least aminimum distance d_(wall) from a wall of the cutout portion 310, inorder to prevent a shunt path (i.e., to reduce capacitive coupling)between rods and the pedestal base 230.

FIG. 4 is an electrical circuit diagram for an RF filter, according toone embodiment described herein. The RF filter 160 may be used invarious embodiments of the substrate support pedestal, pedestal base,and the plasma processing apparatus described above.

As shown, a heating element 150 is coupled to a conductive rod 155 thatextends along the length of the pedestal. In one embodiment, eachconductive rod 155 may be coupled to a respective RF filter 160. The rodis connected to RF filter 160 via connection 240, whose electricalcharacteristics are represented by resistance R10 and inductance L10. Asdescribed above, the connection 240 may be a short rigid lead, or solidwire lead, that is disposed near the pedestal base 230. Capacitance C10represents a feed-through capacitance that occurs where connection 240passes through an opening in a grounded metal enclosure surrounding theRF filter 160. Capacitance C10 may also reflect part of the capacitivecoupling between RF filter components and the grounded metal enclosure.The length of connection 240 may be selected to present a minimalimpedance (i.e., to minimize values of R10 and L10).

The RF filter 160 includes two branches connected in parallel. A firstbranch includes an inductance L20 in series with resistance R20, and asecond branch includes a capacitance C20. Connection 240 is connected inseries at one end of the RF filter 160, and the heating power supply 165is connected at the other end of the RF filter 160. In someconfigurations, a capacitance C30 and the heating power supply 165 areconnected in parallel at one end of the RF filter 160. The capacitanceC30 may represent a second feed-through capacitance occurring when aconnection from the RF filter 160 to the AC power supply passes througha second opening in the grounded metal enclosure, as well as the valueof any discrete capacitors physically connected between the AC powersupply and ground.

The RF filter 160 may have its electrical components selected to providea desired resonance frequency for the RF filter. In one embodiment, theRF filter 160 includes a discrete inductor disposed within a groundedmetal enclosure, which, in some cases, surrounds the various RF filter160 circuit elements. In another embodiment, more than one RF filter 160is included in a shared enclosure. Resistance R20 may representresistive properties of the multi-turn inductor, and capacitance C20 mayrepresent a self-capacitance of the multi-turn inductor (i.e.,capacitance occurring between turns of the inductor), as well ascoupling occurring between the inductor and the conductive enclosure,and between the inductor and other inductors in a shared enclosure. Thenumber of turns of the inductor may be selected to achieve a combinationof desired values for inductance L20 and capacitance C20, so that the RFfilter 160 may exhibit the desired filter response within the heatingassembly. Therefore, in some embodiments, by use of the physicalplacement of the multi-turn inductor L20 relative to a grounded surfaceof the enclosure of the RF filter 160, a relatively fixed and stablecapacitance C20 can be created and used to form part of the RF filtercircuit. In this case, there is no need for the complex and expensivevariable capacitance circuits and/or the need for the unreliablemanually adjusted variable capacitance circuits. However, in someconfigurations, variable capacitance circuits and/or manually adjustedvariable capacitance circuits may be used to form the capacitance C20.

Further, the value of inductance L20 may be selected using the equation:

$\omega = \frac{1}{\sqrt{LC}}$

where w=2π×(the desired resonance frequency of RF filter 160), L=theequivalent inductance of L10 and L20, and C=the equivalent capacitanceof C10, C20, and C30. In one embodiment, capacitance C30 includes adiscrete capacitor having a value that is relatively large compared tothe other capacitances C10 and C20 (or their component capacitances).For example, C30 may include a 47 nano-Farad (nF) capacitor. At typicaloperating frequencies (say, greater than 1 MHz), the reactancecontributed by the 47 nF capacitor will be negligibly small, so that itappears as a short to ground at these frequencies. By eliminating thecontribution of C30, the equation used to determine L20 may thus besimplified to:

$\omega = \frac{1}{\sqrt{L\; 20*( {{C\; 10} + {C\; 20}} )}}$

As will be discussed further below, the resonance frequency of RF filter160 may be selected to provide a desired impedance of the RF filter at aparticular operating frequency of the powered gas distribution manifold.By selecting the resonance frequency in this way, the RF filter 160 maypresent a sufficiently large impedance to prevent RF leakage into theheating assembly and to prevent EMI from being delivered to the heatingpower supply 165 and/or damaging the heating power supply 165.

FIG. 5 illustrates a filter response of an RF filter, according to oneembodiment described herein. Graph 500 depicts the reactance at rod B1of the RF filter 160 (as measured looking into the RF filter) and isplotted as a function of frequency. In this embodiment, the resonancefrequency of RF filter 160 is 12.98 megahertz (MHz), and the operatingfrequency of the powered gas distribution manifold is approximately13.56 MHz. Point 510 shows an approximately zero reactance value at12.98 MHz (where the negative reactance caused by the capacitiveelements of RF filter 160 equals the positive reactance caused by theinductive elements). As the operating frequency shifts away (in eitherdirection) from the RF filter resonance frequency, the magnitude of thereactance value sharply increases to peaks of about 7000 ohms (7 kΩ) atapproximately 12.9 MHz and 13.1 MHz, then gradually decreases. Ofcourse, the sharpness of the slope will depend on the Q factorassociated with the RF filter circuit. For the example operatingfrequency of 13.56 MHz, the reactance value is approximately −2.6 kΩ,indicating a predominantly capacitive reactance for the RF filter atthis frequency.

Based on a given (i.e., known) operating frequency, the resonancefrequency for the RF filter 160 may be selected in order to provide adesired impedance value of the RF filter 160 at the operating frequency.For this example, refer to graph 500 and assume that the filter responsemaintains its basic shape even when shifted left and right to reflectdifferent resonance frequency values. If the resonance frequency isselected to be closer to the operating frequency of 13.56 MHz, forexample 13.45 MHz, the filter response would shift right, and thereactance at 13.56 MHz would be very close one of the peak reactancevalues described above (about −7 kΩ, which is a predominantly capacitivereactance). Of course, the resonance frequency could also be selected tobe greater than the operating frequency, so that the operating frequencyfalls on the predominantly inductive portion of the filter response. Forexample, selecting a resonance frequency of 13.65 MHz would very nearlycorrespond to the other peak reactance value of FIG. 5 (about 7 kΩpredominantly inductive).

Based on the selected resonance frequency, one or more components of theRF filter 160 may be selected. For example, and as described above, RFfilter 160 may include a discrete inductor. To create an RF filterhaving the selected resonance frequency, parameters of the inductor maythen be selected (such as a number of turns, a radius, a length, and soforth). Selecting an electrical component for use in the RF filter 160may also include considering other electrical properties of thecomponent at RF frequencies. For example, an inductor may also exhibitresistive and/or capacitive properties at RF frequencies. The componentsof the RF filter may thus be selected to account for these otherproperties in order to achieve a desired reactance value at theoperating frequency. Of course, selecting RF filter components mayinclude other types of components (resistors, capacitors, etc.) ordifferent combinations or configurations of these components.

As the selected components of the RF filter 160 are installed, forexample installed into a heating assembly prior to operation of theplasma processing apparatus, the components of the RF filter may bepositioned relative to each other, and/or relative to other componentsof the heating assembly, to achieve a desired reactance value for the RFfilter circuit. Based on their positions and orientations, the RF filtercomponents may have capacitive and/or inductive couplings with eachother that may impact the frequency response of the RF filter.Additionally, the RF filter components may be installed into aprotective enclosure, or into an assembly, that may have electricalcharacteristics that cause further couplings impacting the RF filter'sfrequency response. Therefore, the individual components of the RFfilter 160 may each be positioned so that the various couplings can beaccounted for in the resonance frequency. Of course, this may be aniterative process, as moving one component may require adjustment to theproperties of the same component (e.g., selecting a different number ofturns or length) or to other components.

As described above, to achieve a desired impedance of the RF filter 160for a particular operating frequency of the powered gas distributionmanifold, components of the RF filter may be selected (and appropriatelypositioned) that result in the selected filter resonance frequency. Inmost cases, the resonance frequency will differ from the operatingfrequency. However, to ensure that the impedance value is sufficientlylarge to prevent RF energy from coupling into the heating assembly, thefilter resonance frequency should be selected relatively close to theoperating frequency. In one embodiment, the filter resonance frequencymay be selected so that the operating frequency falls within a desiredrange of the resonance frequency. For example, the resonance frequencymay be selected so that the operating frequency falls within ±5% (or±10%) of the resonance frequency. Of course, the ranges could bespecified as frequency differences (e.g., within 1 MHz) instead ofpercentages. In some cases, the resonance frequency may be selected sothat the impedance of the RF filter 160 circuit at the operatingfrequency is a certain desired percentage of the peak impedance (e.g.,7000 Ohms in FIG. 5). In one example, the resonance frequency may beselected so that the impedance of the RF filter 160 circuit at theoperating frequency is between about 10% and 100% of the peak impedance,such as an impedance of between about 15% and 60% of the peak impedance.In one configuration, the operating frequency is within a predeterminedrange that is positioned about the resonant frequency of the RF filter160 circuit. In one example, the operating frequency is within apredetermined range that is defined as being twice the difference of theresonant frequency and a first frequency at which the measured reactanceis within 10% of the peak reactance.

Beyond keeping the operating frequency within a predetermined range ofthe resonance frequency, the resonance frequency may also beadvantageously selected so that the operating frequency is at least aminimum range from the resonance frequency. While the reactance peaksshown in FIG. 5 (corresponding to about 12.9 MHz and 13.1 MHz) eachprovide an attractively large reactance magnitude, selecting theresonance frequency so that the operating frequency falls at or verynear to a reactance peak may not be so beneficial. For example, if theoperating frequency were located on the sharp slope of graph 500(crossing zero reactance at the resonance frequency), any change to theoperating frequency or resonance frequency (which could result fromsmall physical changes during operation, such as deterioration ormovement of components or connections) would result in a large change tothe RF filter impedance. Such large changes of impedance would beundesirable as disturbing the stability of the plasma process, asdifferent and unpredictable amounts and distributions of RF energy wouldbe coupled into the tuning electrode. In some cases, if changes causedthe operating frequency to equal the resonance frequency, the reactanceof the RF filter would equal zero, and a large portion of the RF energycould be coupled into the heater assembly instead of the tuningassembly. Large changes in impedance may also occur near the reactancepeaks on the opposite sides (i.e., less than about 12.9 MHz and greaterthan about 13.1 MHz). Therefore, it may be advantageous to select a RFfilter resonance frequency so that the operating frequency would falloutside some minimum range of the resonance frequency. For example, theresonance frequency may be selected so that the operating frequency isat least ±2.5% (or ±3.5%) of the resonance frequency. In anotherexample, the resonance frequency may be selected so that the operatingfrequency is at least ±2.5% (or ±3.5%) of the resonance frequency, butless than a frequency at which the impedance of the RF filter 160circuit drops to a level of about 10% of the peak impedance.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of processing a substrate, comprising: generating a radiofrequency (RF) plasma in a process volume of a processing chamber;controlling an impedance of a tuning circuit, wherein controlling theimpedance includes minimizing the impedance of a tuning electrodedisposed within a substrate supporting pedestal to ground; and reducingRF coupling between a heater element disposed within the substratesupporting pedestal and the generated RF plasma, wherein the reducingthe RF coupling comprises electrically coupling an RF filter circuitthat comprises a first inductor in parallel with a first capacitance tothe heater element.
 2. The method of claim 1, wherein the RF filtercircuit is disposed within a grounded enclosure.
 3. The method of claim2, further comprising: positioning the first inductor relative to agrounded surface of the grounded enclosure to form the firstcapacitance.
 4. The method of claim 1, wherein minimizing the impedanceof the tuning electrode comprises adjusting a variable capacitorconfigured in parallel with a second inductor.
 5. The method of claim 4,wherein the variable capacitor is further configured in series with athird inductor.
 6. The method of claim 4, wherein the minimizedimpedance of the tuning circuit is less than an impedance of the RFfilter circuit.
 7. The method of claim 4, wherein the heater elementcontrols a temperature profile across a surface of the substratesupporting pedestal.
 8. The method of claim 4, wherein the tuningelectrode is disposed closer to a surface of the pedestal than theheating element.
 9. A method of processing a substrate, comprising:providing an alternating current power to one or more heating elementsdisposed in a substrate support; generating a radio frequency (RF)plasma in a process volume of a process chamber; and adjusting acapacitance of a variable capacitor disposed in an RF tuner coupled to atuning electrode in the substrate support, the variable capacitorterminated to ground through a first inductor.
 10. The method of claim9, wherein the adjusting the capacitance of the variable capacitorreduces an impedance of the RF tuner.
 11. The method of claim 10,wherein the adjusting the capacitance of the variable capacitor controlsa current flow through the tuning electrode disposed in the substratesupport in the process volume.
 12. The method of claim 11, wherein thecapacitance of the variable capacitor is adjusted based on a sensor ofthe RF tuner, and wherein a first terminal of the sensor coupleddirectly to the tuning electrode.
 13. The method of claim 9, whereinadjusting the capacitance of the variable capacitor comprisescontrolling an RF current through the tuning electrode.
 14. The methodof claim 13, wherein adjusting the capacitance of the variable capacitorfurther comprises controlling plasma uniformity in the process volume.15. A plasma processing apparatus, comprising: a chamber body and apowered gas distribution manifold enclosing a process volume; a pedestaldisposed in the process volume, the pedestal having a substratesupporting surface and a stem extending below the substrate supportingsurface; a heating assembly; and a controller configured to perform oneor more operations, the one or more operations comprising: generating aradio frequency (RF) plasma in the process volume; controlling animpedance of a tuning circuit, wherein controlling the impedanceincludes minimizing the impedance of a tuning electrode disposed withina substrate supporting pedestal to ground; and reducing RF couplingbetween a heater element disposed within the substrate supportingpedestal and the generated RF plasma, wherein the reducing the RFcoupling comprises electrically coupling an RF filter circuit thatcomprises a first inductor in parallel with a first capacitance to theheater element.
 16. The plasma processing apparatus of claim 15, whereinminimizing the impedance of the tuning electrode comprises adjusting avariable capacitor configured in parallel with a second inductor. 17.The plasma processing apparatus of claim 15, wherein the tuning circuitcomprises a variable capacitor.
 18. The plasma processing apparatus ofclaim 17, wherein controlling the impedance of the tuning circuitcomprises: controlling a capacitance of the variable capacitor.
 19. Theplasma processing apparatus of claim 18, wherein the minimized impedanceof the tuning circuit is less than an impedance of the RF filtercircuit.
 20. The plasma processing apparatus of claim 18, wherein thetuning electrode is disposed closer to a surface of the pedestal thanthe heating element.